ECONOMIC ENTOMOLOGY 

 PART I 



THE STRUCTURE, GROWTH AND ECONOMICS OF 

 INSECTS 



BRANCH ARTHROPODA (Arthropods) 



Crabs, crayfish and lobsters, spiders and scorpions, centipedes and 

 millipeds have in common with insects jointed appendages and seg- 

 mented, bilaterally symmetrical bodies with a chitinized external skeleton 

 (exo-skeleton) — distinguishing characteristics of the great branch 

 Arthropoda of the Invertebrate animals. These near relatives of 

 insects may be grouped into four classes: 



1. Crustacea. — Aquatic, gill-breathing, wingless Arthropods with 

 two pairs of antennae and at least five pairs of legs. Examples: Crabs, 

 crayfish, lobsters, shrimps, sow-bugs, etc. 



2. Arachnida. — Air-breathing, wingless Arthropods without anten- 

 nae, and usually with four pairs of legs. Examples: Spiders, mites, 

 ticks, and scorpions. 



3. Diplopoda. — Air-breathing, wingless Arthropods with one pair 

 of antennae and numerous body segments each of which bears two 

 pairs of legs. The mouth-parts consist of a pair of mandibles and a 

 compound plate. Example: Millipeds. 



4. Chilopoda. — Air-breathing, wingless Arthropods with one pair 

 of antennae and numerous body segments each bearing one pair of 

 legs. The mouth-parts consist of one pair of mandibles and two pairs 

 of maxiUas. Example: Centipedes. 



(Classes 3 and 4 are frequently grouped as sub-classes of the class 

 Myriapoda.) 



